The extraction of acetic acid from aqueous solutions by tri-n-octylamine dissolved in various diluents in wide range of amine concentration (0.23 - 1.15 mol / L) is studied. Extraction equilibria of acetic acid in the solution of tri-n-octylamine in five various. solvents at 298.15 K is measured., Diluting solvents used in this study are hexane, cyclohexane, toluene, methyl isobutyl ketone (MIBK), and propanol. Using Bizek approach two acids: amine complexes, (Acid), (Amine) and (Acid), (Amine)(2) is are assumed to exist in the organic phase in the case of proton - donating diluents, while the complexes (Acid), (Amine) and (Acid) (2), (Amine)(3) are suggested in the case of non-proton-donating diluents. As a result of batch extraction experiments, distribution coefficients (D), loading factors ( Z), and overall extraction constants (K-11, K-12, K-23) are calculated.